Multi-modal particle detector

ABSTRACT

Systems, methods and computer program products for the multi-modal detection of particles are described herein. An embodiment of the present invention is a particle detector that includes a first chamber wherein analyte particles are subjected to a first particle detection mechanism, and a second chamber coupled to the first chamber, wherein the analyte particles are subjected to a second particle detection mechanism, and wherein the detection characteristics of second particle detection mechanism are orthogonal to detection characteristics of the first particle detection mechanism. According to another embodiment, the present invention is a particle detection method including the steps of detecting presence of at least one predetermined particle type in an analyte particle sample using a first particle detection mechanism, and confirming the presence of the predetermined particle type in the analyte particle sample using a second particle detection mechanism, wherein detection characteristics of the second particle detection mechanism are orthogonal to detection characteristics of the first detection mechanism.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to threat detectors, and moreparticularly to multi-modal particle detectors for detecting chemical,biological, and explosives threats.

2. Background Art

The detection of chemical, biological, and explosives threats isbecoming increasingly difficult due to the continuously changing natureof such threats. For example, new combinations of chemicals are used forexplosives, new delivery mechanisms are used with lethal chemical andbiological compounds, and new constructions are employed for improvisedexplosives devices (IED). Detection is also made difficult due tothreats arising in environments or locations that are not conducive fordeploying traditional threat detection mechanisms.

Many threat detection devices are described in the art. For example, thebackground section of U.S. Pat. No. 6,610,977 ('977 patent), which isincorporated herein by reference in its entirety, includes an extensivedescription of various threats and threat detection mechanisms.Generally, threat detection mechanisms may be classified into trace andbulk detection. In trace detection, minute quantities of materials aredetected either in vapor or particulate form. The related tracedetection mechanisms include electron capture, gas chromatography, massspectroscopy, ion mobility spectrometry, Raman spectroscopy, plasmachromatography, biological markers and laser photo acoustics. Tracedetection mechanisms are primarily suited for detection of threatsubstances in the environment. Bulk detection mechanisms are primarilyused to detect bulk quantities of threat substances that are concealedand carried in various forms, including baggage. They include x-ray,gamma-ray, neutron activation and nuclear magnetic resonance.

Despite the large number and variety of threat detectors that arecommercially available, there is a paucity of multi-modal detectors thatare capable of detecting multiple threats based on different propertiesof threat particles. To be effective, multi-modal detectors must detectthreat particles efficiently and with reduced false alarm rates for avariety of threat particles, while also being capable of flexibledeployment in various environments. Some attempts at developingmulti-modal detectors have been made. For example, the '977 patentdiscloses a combination of multiple known detectors in a predetermineddecision hierarchy. U.S. Pat. No. 5,668,342 ('342 patent) discloses amethod of detecting multiple types of explosives materials byilluminating that material with multiple energy sources. The '977 patentcombines different sensors as they are without an effort to increase theefficiency available by integration of selected techniques, and withoutan effort to increase the ability to deploy. The '342 patent onlyaddresses the detection and neutralization of explosives in baggagecheck applications.

What is needed therefore, is a multi-modal particle detector that iscapable of efficiently detecting multiple types of threats includingchemical, biological, and explosives threats with reduced false alarmrates, and is capable of being deployed reliably in a number ofdifferent environments.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to systems, methods and computerprogram products for multi-modal particle detectors. Briefly stated, aparticle detector system embodiment of the present invention includes aparticle detector that includes a first chamber wherein analyteparticles are subjected to a first particle detection mechanism, and asecond chamber, coupled to the first chamber, wherein the analyteparticles are subjected to a second particle detection mechanism, andwherein the detection characteristics of second particle detectionmechanism are orthogonal to detection characteristics of the firstparticle detection mechanism.

According to another embodiment, the present invention is a particledetection method including the steps of detecting presence of at leastone predetermined particle type in an analyte particle sample using afirst particle detection mechanism, and confirming the presence of thepredetermined particle type in the analyte particle sample using asecond particle detection mechanism, wherein detection characteristicsof the second particle detection mechanism are orthogonal to detectioncharacteristics of the first detection mechanism.

Further features and advantages of the present invention, as well as thestructure and operation of various embodiments thereof, are described indetail below with reference to the accompanying drawings. It is notedthat the invention is not limited to the specific embodiments describedherein. Such embodiments are presented herein for illustrative purposesonly. Additional embodiments will be apparent to persons skilled in therelevant art(s) based on the teachings contained herein.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

FIG. 1 is a multi-modal detector according to an embodiment of thepresent invention.

FIG. 2 is an example graph showing the effectiveness of combining highlyorthogonal detection mechanisms, specifically IMS and SERS. The graph ofFIG. 2 may be derived, for example, from the output of a multi-modaldetector of FIG. 1.

FIG. 3 is a flowchart illustrating the operation of a multi-modaldetector according to an embodiment of the present invention.

FIG. 4 is a flowchart illustrating the operation of an IMS component ofa multi-modal detector according to an embodiment of the presentinvention.

FIG. 5 is a flowchart illustrating the operation of a SERS component ofa multi-modal detector according to an embodiment of the presentinvention.

FIG. 6 is a flowchart of steps implemented in a control module tocombine the characteristic particle data received from an IMS componentand a SERS component of a multi-modal detector according to anembodiment of the present invention.

FIG. 7 is an example computer that may implement the system andcomponents of the present invention according to an embodiment.

The features and advantages of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings. In the drawings, like reference numbersgenerally indicate identical, functionally similar, and/or structurallysimilar elements. Generally, the drawing in which an element firstappears is indicated by the leftmost digit(s) in the correspondingreference number.

DETAILED DESCRIPTION OF THE INVENTION 1. Overview

The present invention relates to embodiments of multi-modal detectorsfor the detection of multiple threats. While the present invention isdescribed herein with reference to illustrative embodiments forparticular applications, it should be understood that the invention isnot limited thereto. Those skilled in the art with access to theteachings herein will recognize additional modifications, applications,and embodiments within the scope thereof and additional fields in whichthe invention would be of significant utility.

A key to effective multi-modal threat detection and reduction of falsealarms is the use of multiple detection mechanisms in an efficient andintegrated manner. For example, embodiments of the present inventionintegrate the use of ion mobility spectrometry (IMS) detection withsurface enhanced Raman spectroscopy (SERS). The two particle detectionmechanisms, IMS and SERS, are selected due to the orthogonal detectionproperties of each mechanism. For example, IMS detection is based onmobility properties of particles, while SERS detection is based on thelight scattering properties. By combining orthogonal detectioncharacteristics, the efficiency of detection and also the range ofthreat substances detectable are increased.

IMS technology is generally well known in the art. Similarly, theconstruction of a standalone IMS particle detector is well known. Forexample, U.S. Pat. No. 6,969,851, which is incorporated herein byreference in its entirety, outlines the construction of an IMS sensorfor detecting a particular gaseous substance. An IMS detector includesan ionization region and a drift region. A shutter grid is placedbetween the two regions so that the flow of analyte particles from theionization region to the drift region can be controlled. Analyteparticles are ionized in the ionization region. Subsequently samples ofionized analytes make their way through the shutter grid into the driftregion. Ionized analytes are accelerated in the drift cell by anelectric field and are simultaneously slowed down due to collisions withthe background drift gas. This results in a characteristic drift timefor a specific analyte module. Detection, for example, collectorelectrodes at the end of the drift region, is triggered when the ionizedparticles strike the electrodes. A current may be generated inproportion to the number of ionized particles striking the collectorelectrodes at a given instant. IMS measures the drift time of eachparticle, which is defined by the time interval between the particleentering the drift chamber 122 and arrival at the collector electrodes124. The characteristic drift times for a variety of particle types maybe known to the device through reference data.

SERS technology and the construction of a standalone SERS detector arealso well known in the art. A SERS detector, in general, includes alight source, an optical light collection and detection mechanism, and aSERS substrate upon which analyte particles are accumulated and uponwhich a photon beam generated by the light source is irradiated. Thescattered light from the vibrationally excited analyte molecules on theSERS substrate surface is monitored by the optical detection mechanismto detect the characteristic Raman spectra typical to known particletypes. Raman spectroscopy is a mechanism that measures the inelasticscattering of optical (photon) energy resulting in a shift in thefrequency of the incident light and thus resulting in spectral peaksthat correspond to photon energy different from those of the energy ofthe incident photons on the analyte particles. The scattered Ramansignals arise as a result of changes (with respect to time) inpolarization in particles due to vibrational excitation of the moleculesby the incident light, yielding unique and characteristicstructurally-specific Raman signal fingerprints to most particles. Theintensities of Raman bands are substantially dependent on the intensityof the local electric field and the number of particles with thecorresponding vibration state. Also, due to very narrow line-width ofnatural Raman spectral lines the inherent high resolution of Ramanspectra allows the simultaneous analysis of multiple particle types.SERS is a variant of Raman spectroscopy that yields highly enhancedRaman signals due to the special engineering of the substrates and hasthe requisite sensitivity to detect particles in small or tracequantities of samples, without multiple passes of the analytes throughthe detection mechanism or long acquisition times. A detector, such asthe present invention in one embodiment, due to its small size, ease ofdeployment, and portability must have a high level of sensitivity evento small sample quantities. SERS methods allow analyte particles to beadsorbed into substrates including nanometer-size metallic particleslike silver, copper and gold, which substantially enhances the intensityof the scattered Raman light, thus making it practical to obtaincharacteristic Raman fingerprints for particles with small samplequantities.

By combining detection mechanisms with highly orthogonal detectioncharacteristics, such as but not limited to those described herein,embodiments of the present invention minimize the risks of falsedetection and faulty identification. Furthermore, by placing an IMSdetector in front of a SERS detector, embodiments of the presentinvention are designed to utilize IMS as a speedy filtering mechanismand to selectively subject identified samples for the more rigorous SERSdetection. Threat particles that cannot be sufficiently distinguishedusing only IMS may be distinguished by using both its IMScharacteristics and SERS characteristics. By activating SERS detectiononly as needed, embodiments of the present invention leverage therelatively more sensitive SERS detection equipment in an efficientmanner. Embodiments of the present invention may be constructed inminiaturized form and in other forms suitable for portability anddeployment in various environments including environments demandingunmanned deployment.

Example embodiments for achieving multi-modal threat detection accordingto the present invention are described in the following sections.

2. Composition of the Multi-Modal Detector

FIG. 1 illustrates a multi-modal particle detector 100 according to anembodiment of the invention. Example multi-modal detector 100 includesan IMS particle detector in a first chamber 120 and a SERS detector in asecond chamber 130. Sample analytes subjected to IMS detection in thefirst chamber 120 may be selectively subjected to further SERS detectionin the second chamber 130.

The first chamber 120 includes an ionization region 121 and a driftregion 122. The ionization region 121 includes a specimen intake 111where the analyte specimen is introduced into the IMS detector 120 andan ionization source 160. The ionization source 160 may include a radioactive substance such as nickel-63 (⁶³Ni), an electrospray ionizer, or aspark electrode ionizer. An optional sample collection attachment 110may be integrated to detector 100 which includes a vacuum pump orsimilar suction device to assist in the collection of the analyte samplefrom the environment. The sample can also be obtained by swiping thesurface of the threat object (that needs to be examined) or byadditional means that allow releasing particles from a surface, such asby impinging an air jet, by striking strobe light or otherelectromagnetic pulses such as terahertz radiation. The drift region 122may include collector electrodes 124 that measure particles, a drift gasreservoir 170, and a drift gas outlet 171. A shutter grid 123 separatesthe ionization region 121 from the drift region 122 and includes thecapability to allow controlled amounts of ionized samples into the driftregion 122. When shutter grid 123 is open analytes enter from theionization region 121 and flow through the drift region 122 under theguidance of an electric field. A drift gas, collected in the drift gasreservoir 170 and injected into the drift region 122 through the driftgas outlet 171, flows in the direction opposite to the analyteparticles. Analyte particles travel through the drift region 122 atspeeds characterized by particle type and collide with the collectorelectrodes 124 that generate an electrical signal proportional to theintensity of the particle collisions. The IMS characteristics of theanalyte particles are determined based on the signal generated by thecollector electrodes 124. The collector electrodes 124 may include ashutter mechanism whereby particles are allowed into the second chamber130 in controlled time intervals. For example, in one embodiment,instead of having particles collide with the collector electrodes 124,the collector electrodes 124 may momentarily move apart to uncovershutter 125 which is an opening to the second chamber 130.

The second chamber 130 includes a SERS substrate 131, a light source132, and an optical detector 133. The SERS substrate 131,is generallyplaced at the far end from shutter 125. In another embodiment, the SERSsubstrate 131 may be placed on a precision position manipulationplatform that may, for example, be controlled by the control module 140such that detection is optimized. The light source 132 may include akrypton-ion laser, near infrared diode laser, or Nd:YAG laser thatgenerates light signals having wavelengths in the range, by way ofexample and without limitation, from 532 to 1064 run. Optionally, a beamfocusing device 134 and a substrate refresher device 135 may beincluded. Beam focusing device 134 can be used to focus the ion beamsuch that particle concentration on localized areas on the SERSsubstrate is enhanced. A method, such as, for example, the well knownmethods of focusing with electrostatic quadrupole lenses or ion beamfunneling can be used in device 134. Ion beam funneling is described,for example, in Keqi Tang, Alexandre A. Shvartsburg, Hak-No Lee, DavidC. Prior, Michael A. Buschbach, Fumin Li, Aleksey V. Tolnachev, GordonA. Anderson, and Richard D. Smith, “High-Sensitivity Ion MobilitySpectrometry/Mass Spectrometry Using Electrodynamic Ion FunnelInterfaces,” Analytical Chemistry, pp. 3330-3339 Vol. 77 (2005). Theoptional substrate refresher device 135 can enhance the reusability ofthe SERS substrate. For example, device 134 can utilize a technique toreleasing particulates such as, for example, use of an air jet, use ofan energy transfer medium including water droplets or a mixture of waterand alcohol, and dry removal by laser. A method of dry removal by laseris described in U.S. Pat. No. 4,987,286 that is incorporated byreference herein in its entirety. Embodiments of the present inventionmay include additional optical devices or mechanisms to focus the lightbeam between the light source 132 and SERS substrate 131, and also toenhance signal detection between SERS substrate 131 and optical detector133. When the light source 132 is active and focused on the SERSsubstrate 131, analytes that collide with the SERS substrate 131 emitRaman signals that are then detected by the optical detector 133.

Both detectors, the IMS detector in the first chamber 120 and the SERSdetector in the second chamber 130, of the example multi-modal particledetector 100, may be coupled to a control module 140. The control module140 may control and coordinate events in the first chamber 120 and thesecond chamber 130. The control module 140 may also receive particledata from both detectors and combine and analyze the received particledata. For example, the received particle data may be combined in amanner that increases the likelihood of definitive identification ofanalyte particles. The combined results may be displayed in anoptionally coupled display 150. FIG. 2 illustrates an example graph 200that may be displayed on display 150. Graph 200 shows five analytecompounds with their characteristics plotted according to thecharacteristic ion mobility values from IMS detection on the Y-axis, andaccording to the characteristic Raman shift values from SERS detectionon the X-axis.

The control module 140 may control, for example, the specimen intake 111to control when sample analytes are input and in what quantity, theionization source 160 to control when analyte samples are ionized, theshutter grid 123 to control the timing and volume of ionized samplesallowed into the drift region 122, the activation and strength of theelectric field in the drift region 122, the acquisition of drift gas incomponent 170, the injection of drift gas through outlet 171, themonitoring of the collector electrodes 124 to measure the signalgenerated, the manipulation of the collector electrodes 124 and shutter125 to allow analyte particles to flow through to the second chamber 130at controlled intervals, the activation of the light source 132, and themonitoring of the optical detector 133 to measure and identify the Ramanspectra that are generated. Identification may require cross-checkingthe measured spectra with a reference spectral library. Also, thecontrol module 140 may include control logic for combining the signalsgenerated from the IMS detector's collector electrodes 124 and the SERSdetector's optical detector 133. Control module 140, in embodiments ofthe present invention, may be coupled to the first chamber 120, secondchamber 130, and display 150 through wired or wireless communicationchannels and also may be distributed over multiple platforms.

The operation of this embodiment shall now be described in greaterdetail with reference to flow charts 300, 400, 500, and 600 in FIGS. 3,4, 5 and 6 respectively. For illustrative but non-limiting purposes, theflowcharts 300, 400, 500, and 600 shall be described with continuingreference to the example multi-modal particle detector 100. Flowchart300 of FIG. 3 illustrates the overall operation of the multi-modalparticle detector 100. In step 310 samples of the analyte particles arefirst subjected to IMS detection in the first chamber 120. Furtherdetails of processing in step 310 are described below with respect toflowchart 400. The resulting particle data from IMS detection isreceived by control module 140 and a determination may be made, in step320, if further analysis of the analyte is required. The determinationin step 320 may be based on the particular IMS measurements beingobserved, analysis of the measured data and cross checking with areference library of mobility values. For example, if the IMSmeasurement corresponds to an ion mobility value of approximately 1.5cm²V⁻¹s⁻¹ in a sample for air or nitrogen as drift gas, the controlmodule 140 may determine that it is not possible to clearly determine ifthe analyte substance is a threat substance such as TNT or RDX or anon-threat substance such as dinitro-o-cresol (DNOC) unless alaboratory-scale high-resolution IMS is used. If it is determined instep 320 that further analysis is necessary, then in step 330 samples ofthe analyte are subjected to SERS detection in the second chamber 130. Adetailed description of processing within a SERS detector is providedbelow with respect to flowchart 500. The resulting particle data of theSERS detection is received by control module 140. Control module 140combines the IMS particle data and the SERS particle data. In step 340control module 140 may output the combined particle data to display acombined graph on display 150. Graph 200 of FIG. 2 is an example graphthat integrates IMS particle data and SERS particle data in such amanner as to facilitate definitive determination of the analyteparticles.

3. IMS Detection in the Multi-Modal Detector

In FIG. 4, the flowchart 400 illustrates the processing within the IMSdetector in the first chamber 120 of the multi-modal detector 100. Instep 410 an analyte sample is input to the IMS detector's ionizationregion 120 through specimen intake 111. Embodiments of the presentinvention may include a sample collection attachment 110. It should benoted that there are many well known methods of acquiring a suitableanalyte sample to be input through specimen intake 111. For example, ifthe analyte particles are airborne in the environment, an adequatespecimen may be collected with or without the aid of a vacuum pump orsimilar environment air suction device implemented in an optional samplecollection attachment 110. In another embodiment of the presentinvention, a heating element placed in the sample collection attachment110 may be used to release analyte particles from a specimen intospecimen intake 111.

In step 420, particles in the ionization region 121 are ionized. In someembodiments, an ionization source 160 is used. One of several ionizationsources 160 may be used to achieve the ionization of analyte particles.For example, a radio active substance such as nickel-63 (⁶³Ni) may beused, where the β-particles released by ⁶³Ni collide with particles inthe sample, such as nitrogen and oxygen. The ionized particles thenreact with the analyte particles being examined, and analyte ions areformed. In another embodiment, a soft ionization technique, for example,electrospray ionization may be utilized where less fragmentation ofanalyte particles occur. In yet another embodiment of the presentinvention, ionization may be caused by the use of an electric discharge.For example, the ionization region 121 may have as the ionization source160 a spark electrode coupled to a voltage source that enables thecreation of spark discharge. The spark discharge triggers ionization ofanalyte particles along with other particles of the specimen. U.S. Pat.No. 6,969,851, incorporated herein by reference in its entirety,includes an implementation of ionization by the use of an electricdischarge. Other ionization techniques that may be used in embodimentsof the present invention include photo-ionization, corona dischargeionization and ionization by the use of an electric discharge.Ionization techniques and the implementation thereof are well known inthe art.

In step 430, an electric field may be activated. The electric field may,for example, exist between the left wall of the ionization region 121and the right wall of the drift region 122. The electric field issubstantially uniform. A purpose of the electric field is to encouragethe movement of the ionized analytes from the ionization region 121 intothe collector electrodes 124 in the drift region 122. In anotherembodiment, the electric field may exist between the left and rightwalls of the drift region 122. U.S. Pat. No. 4,378,499, incorporatedherein by reference in its entirety, describes methods of generating anelectric field.

The shutter grid 123 is opened in step 440 to allow ionized analytes toenter the drift region 122. For example, in the embodiment illustratedin multi-modal detector 100 the ionized particles may be kept in theionization region 121 by biasing the inside of the ionization region 121and the shutter 123 with the same polarity as the ionized particles.When a sample of the ionized particles is to be released into the driftregion 122 the shutter grid 123 may be momentarily biased with theopposite polarity so that the ionized particles are drawn towards it.The direction of electric field is appropriately established so that theanalyte ions of a particular polarity can pass through the shutter gridand are accelerated in the drift cell. The shutter grid is then openedallowing the ionized particles to move into the drift region. Theshutter is generally made of thin mesh wires with a bias voltage betweenthem. When the bias voltage is turned on, the ions are attracted to thegate and lose their charge. When the bias voltage is turned off, theions are released into the drift region. U.S. Pat. No. 4,777,363,incorporated herein by reference in its entirety, discloses a particulartype of ion-gate known as a Bradbury-Nielson arrangement which may beused in an embodiment of the present invention. In another embodiment ofthe present invention, the shutter grid 123 may be an electro-mechanicaldevice operated by an electrical pulse where the analyte particles aredrawn to the drift region 122 due to the electric field in the driftregion 122.

Analyte particles flowing into the drift region 122 through the openshutter grid 123 move across the drift region 122. The analyte particlesin drift region 122 move parallel to a uniform electric field in thedrift region 122. At the opposite end from the shutter grid 123, theanalyte particles make contact with the collector electrodes 124. Thedrift region 122 may have a length of about 8 cm and may have asubstantial electric field, for example, of several hundred volts percentimeter. In one embodiment, the drift region 122 is 4 cm in lengthand 3 cm in diameter. The particles, guided by the electric field in thedrift region 122, arrive at the collector electrodes 124. The electricfield in the drift region 122 is substantially uniform. Generally,particles travel at a speed that is determined by their size, mass andgeometry, and further affected by the specific drift medium includingthe electric field within the drift region 122. In general, smaller ionstravel faster than the larger ions, as they traverse the drift regionand collide with the collector electrodes 124. For each IMS device, ingeneral the drift time for each type of particle is known. The currentgenerated at collector electrodes 124 is proportional to the number ofions that collide over time. The collector electrodes 124 in theembodiment illustrated in multi-modal detector 100 may be implemented asa Faraday plate. For example, U.S. Pat. No. 4,390,784, incorporatedherein by reference in its entirety, discloses a particular design ofcollector electrodes 124. In general, a processor may monitor the signalgenerated by the collector electrodes 124 to determine the type ofparticles based on the drift duration of each particle colliding withthe collector electrodes 124. For example, the strength of theelectrical signal generated over time, when related to the expecteddrift time of each particle type will yield a measure of the compositionof particles contained in the sample. In step 450, the IMScharacteristics of analyte samples are monitored using methodsincluding, for example, the monitoring of the current generated by thecollector electrodes 124.

Within the drift region 122, the ionized particles interact with driftgas particles that are separately injected into the drift region 122.The drift gas may be clean dehumidified air. In one embodiment of thepresent invention, a drift gas inlet 171 is situated below the collectorelectrodes 124. The drift gas inlet 171 may be connected to a drift gasacquisition device 170. In the example embodiment illustrated inmulti-modal detector 100, drift gas acquisition device 170 may be adevice that dehumidifies and filters air obtained from the environment.The drift gas, injected from the drift gas inlet 171, flows in thedirection opposite to analyte particles. The drift gas may pass throughshutter grid 123 in the direction opposite to analyte particles and exitthe ionization region 121 through specimen intake 111. A person skilledin the art will understand that many alternative designs are possiblefor the drift gas inlet 171 and drift gas acquisition device 170.

In an embodiment of the present invention, the capability exists tooperate the IMS detector in a mode where the analytes are collected atthe collector electrodes 124 or in a mode where the analytes are allowedto bypass the collector electrodes 124 to the SERS detector and enterthe second chamber 130 through shutter 125. An embodiment of the presentinvention includes the ability to use the IMS detector in the firstchamber 120 to make a preliminary determination of the level of interestin the sample being analyzed, and if the sample meets certain criteriaof interest, for example, having IMS detect the presence of acomposition of analyte particles as determined by comparing the mobilityvalue from the measured IMS data with that from the reference library,to enable further analysis using SERS in the second chamber 130. Due tothe orthogonal nature of IMS and SERS detection characteristics, furtheranalysis using SERS would confirm, in many cases, the composition ofanalyte particles initially determined using IMS. One aspect of theefficiency of the multi-modal detector 100 is the use of IMS detectionequipment as a filter to limit the use of SERS detection equipment. Ingeneral, IMS equipment can yield high sensitivity and rapid responsetimes, and are robust to use, whereas SERS equipment have highsensitivity, high chemical specificity, and lower robustness. Tofacilitate the passage of the analyte particles to the second chamber130, the collector electrodes 124 may be momentarily moved to exposeshutter 125 at the instruction of the control module 140. In anotherembodiment of the present invention, a separate path may be provided toinject particles into the second chamber 130 upon instruction by thecontrol module 140. For example, a separate path may be constructed fromthe analyte intake region 111 to the second chamber 130 that bypassesthe IMS drift region 122.

Control module 140 may be configured to allow the passage of certainanalyte particles from the first chamber 120 to the second chamber 130.Only an analyte sample likely to contain a predetermined set ofparticles, as determined by the IMS detector in the first chamber 120,may be allowed into the second chamber 130. This allows the SERSdetector in the second chamber 130 to be activated only as needed toanalyze initial determinations made by the IMS detector in the firstchamber 120.

4. SERS Detection in the Multi-Modal Detector

In FIG. 5, the flowchart 500 illustrates the processing within the SERSdetector in the second chamber 130 of the multi-modal detector 100. Whena determination is made in step 320 that further analysis of the analytesample is required, control module 140 may, in step 510, activate theSERS detector in the second chamber 130. For example, the light source132 may be activated, the SERS substrate may be heated, and opticaldetector 133 may be focused prior to the entry of the analytes into thesecond chamber 130 from the first chamber 120. In step 520 analyteparticles are allowed into the second chamber 130. Analyte particlesflow through the second chamber 130 and deposit on the SERS substrate131. In step 530, light source 132 is irradiated on the SERS substrate.Analytes that are present on the SERS substrate 131 when light source132 is irradiated get vibrationally excited due to the enhanced localelectric field at the SERS substrate 131 and generate characteristicRaman signals. In step 540, Raman signals are detected at opticaldetector 133. A person skilled in the art will understand that someembodiments of the present invention may include devices to enhancedetection, for example, focusing lenses or collimating lenses, asintermediate devices between the SERS substrate 131 and optical detector133. Some embodiments of the present invention may also includeintermediate collection optical fibers between the SERS substrate 131and optical detector 133, as well as filters that reduce backgroundfluorescent light. Optical detector 133 generates a signal indicative ofthe spectral components detected in the Raman signals. In step 550, theSERS characteristics of the analyte particles may be monitored throughRaman signals received at optical detector 133. The output signalrepresenting the detected spectral components, generated by the opticaldetector 133, may be received by control module 140. The control module140 may further filter secondary Raman signals and noise from thesubmitted signal, for example, by the execution of a software computerprogram. The control module 140 may further ascertain the specific typeof particles contained in the sample. For example and withoutlimitation, software programs may be used to analyze the Raman signalsto determine the specific mix of analytes contained in the sample ofparticles.

Light source 132 may be implemented as a krypton-ion laser, nearinfrared diode laser, or Nd:YAG laser that generates light signalshaving wavelengths in the range, by way of example and withoutlimitation, from 532 to 1064 nm. In one embodiment, for example as inmulti-modal detector 100, a 785 nm laser with a milliwatt power levelmay be used. The light signal generated by light source 132 is focusedon the surface of SERS substrate 131. A person skilled in the art willunderstand that, in some embodiments of the present invention, there maybe, for example, an optical fiber between light source 132 and SERSsubstrate 131 to guide the light signal and/or a filter or lens to focusthe light signal on to the SERS substrate 131.

5. Control of the Multi-Modal Detector

Control module 140 directs the operation of multi-modal detector 100.For example, processing in control module 140 may include triggering theopening of shutter grid 123 and collector electrodes 124, controllingthe activation of the ionization source 160, regulating the drift region122 electric field, activating the light source 132, and the collectionof analyte information from collector electrodes 124 and opticaldetection device 133. Control module 140 may have access tocharacteristic IMS drift times as well as characteristic Raman spectrafor a plurality of analyte particle types. Analyte data received fromthe collector electrodes 124 and optical detector 133 may be matchedagainst known characteristic IMS drift times and Raman spectra to makedeterminations. Control module 140 includes control logic to receive,combine and analyze particle data from the IMS detector in the firstchamber 120 and the SERS detector in the second chamber 130. Thecombination of the results received from the two detectors enable thepresentation of that data in such a way as to distinguish the componentscontained in the analyte sample. The functionality of the control module140 may be implemented in software and executed on one or moreprocessors. In some embodiments, control module 140 may include hardwareor firmware components to assist in some of the processing. For example,the collection of the SERS detected Raman spectra and the matching ofthe collected spectra to the predefined spectra may be performed by aspecialized processor. In yet another embodiment of the presentinvention, the first chamber 120 and the second chamber 130 may eachhave its own dedicated processor to control the respective detectionmechanism and collect analyte data. The data may then be combined toproduce a combined graph.

Control module 140 may also control a display 150. Display 150 maydisplay a two-dimensional graph of properties of each analyte type. Inone embodiment of the present invention, the two dimensional graph ofFIG. 2 may be generated by control module 140 and displayed in display150. Graph 200 illustrates one clear advantage of the presentinvention—that of being able to clearly differentiate between analytesthat may display very similar characteristics in one detectionmechanism. For example, in graph 200, TNT, RDX and DNOC display veryclose IMS drift times as indicated on the Y-axis, but have substantiallydifferent Raman characteristics. Similarly, HMX and musk ambrette (acommon ingredient in perfumes) display very close IMS drift times whilesubstantially differing in Raman characteristics. Although Ramansignals, in general, show significantly better characteristic featuresthan IMS, the Raman spectroscopy alone can have difficulty to identifymultiple analytes simultaneously in a mixed sample which is typicallythe case in field applications. IMS data allows some separation amongthe components and significantly enhances the processing of the Ramanspectra. The integrated display of particle data yielded by these twohighly orthogonal detection methods make the determination of theanalyte composition more efficient, and reduces the risk of falsepositives. The Raman shift data illustrated in FIG. 2 is derived fromBrian Eckenrode, Edward G. Bartick, Scott D. Harvey, Mark E. Vucelick,Bob W. Wright, Rebecca A., “Portable Raman Spectroscopy Systems forField Analysis”, Huff, Forensic Science Communications, Vol. 3, No. 4(October 2001), and Process Instruments, “PI-200 Raman SpectrometerApplications” at www.process-instruments-inc.com/pages/energetics.html(last visited on Mar. 10, 2008). The IMS mobility data in FIG. 2 is fromLaura M. Matz, Pete S. Tomatore and Herbert H. Hill, Talanta,“Evaluation of suspected interferents for TNT detection by ion mobilityspectrometry,” pp. 171-179, Vol. 54 (2001) and R. G. Ewing, D. A.Atkinson, G. A. Eiceman, G. J. Ewing, Talanta, “A critical review of ionmobility spectrometry for the detection of explosives and explosiverelated compounds,” pp. 515-529, Vol. 54 (2001).

FIG. 6 illustrates a flowchart 600 that shows, in one embodiment, stepsimplemented by control module 140 to combine the particle data receivedfrom the IMS detector in the first chamber 120 and the SERS detector inthe second chamber 130. During or immediately subsequent to the IMSdetection phase illustrated in flowchart 400, control module 140 mayreceive, in step 610, IMS particle data for the analyte sample underconsideration. In step 620 control module 140 receives SERS particledata for the analyte sample under consideration. SERS particle data maybe collected by control module 140 either during or immediately afterthe SERS detection phase illustrated in flowchart 500. In step 630 thecontrol module 140 may combine the IMS particle data and the SERSparticle data, as they refer to the same analyte compounds. The combinedparticle data may be illustrated, for example, in a graph 200 designedto differentiate among analyte compounds according to the strength ofeach detection mechanism. According to some embodiments, in step 640,graph 200 may be displayed in a coupled display 150.

6. Example Computer Embodiment

In an embodiment of the present invention, the system and components ofthe present invention described herein are implemented using well knowncomputers, such as computer 702 shown in FIG. 7. For example, controlmodule 140 can be implemented using computer(s) 702.

The computer 702 includes one or more processors (also called centralprocessing units, or CPUs), such as a processor 706. The processor 706is connected to a communication bus 704.

The computer 702 also includes a main or primary memory 708, such asrandom access memory (RAM). The primary memory 708 has stored thereincontrol logic 728A (computer software), and data.

The computer 702 may also include one or more secondary storage devices710. The secondary storage devices 710 include, for example, a hard diskdrive 712 and/or a removable storage device or drive 714, as well asother types of storage devices, such as memory cards and memory sticks.The removable storage drive 714 represents a floppy disk drive, amagnetic tape drive, a compact disk drive, an optical storage device,tape backup, etc.

The removable storage drive 714 interacts with a removable storage unit716. The removable storage unit 716 includes a computer useable orreadable storage medium 724 having stored therein computer software 728B(control logic) and/or data. Removable storage unit 716 represents afloppy disk, magnetic tape, compact disk, DVD, optical storage disk, orany other computer data storage device. The removable storage drive 714reads from and/or writes to the removable storage unit 716 in a wellknown manner.

The computer 702 may also include input/output/display devices 722, suchas monitors, keyboards, pointing devices, etc.

The computer 702 further includes at least one communication or networkinterface 718. The communication or network interface 718 enables thecomputer 702 to communicate with remote devices. For example, thecommunication or network interface 718 allows the computer 702 tocommunicate over communication networks or mediums 724B (representing aform of a computer useable or readable medium), such as LANs, WANs, theInternet, etc. The communication or network interface 718 may interfacewith remote sites or networks via wired or wireless connections. Thecommunication or network interface 718 may also enable the computer 702to communicate with other devices on the same platform, using wired orwireless mechanisms.

Control logic 728C may be transmitted to and from the computer 702 viathe communication medium 724B. More particularly, the computer 702 mayreceive and transmit carrier waves (electromagnetic signals) modulatedwith control logic 730 via the communication medium 724B.

Any apparatus or manufacture comprising a computer useable or readablemedium having control logic (software) stored therein is referred toherein as a computer program product or program storage device. Thisincludes, but is not limited to, the computer 702, the main memory 708,secondary storage devices 710, the removable storage unit 716 and thecarrier waves modulated with control logic 730. Such computer programproducts, having control logic stored therein that, when executed by oneor more data processing devices, cause such data processing devices tooperate as described herein, represent embodiments of the invention.

The invention can work with software, hardware, and/or operating systemimplementations other than those described herein. Any software,hardware, and operating system implementations suitable for performingthe functions described herein can be used.

7. Conclusion

It is to be appreciated that the Detailed Description section, and notthe Summary and Abstract sections, is intended to be used to interpretthe claims. The Summary and Abstract sections may set forth one or morebut not all exemplary embodiments of the present invention ascontemplated by the inventor(s), and thus, are not intended to limit thepresent invention and the appended claims in any way.

The present invention has been described above with the aid offunctional building blocks illustrating the implementation of specifiedfunctions and relationships thereof. The boundaries of these functionalbuilding blocks have been arbitrarily defined herein for the convenienceof the description. Alternate boundaries can be defined so long as thespecified functions and relationships thereof are appropriatelyperformed.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the invention that others can, by applyingknowledge within the skill of the art, readily modify and/or adapt forvarious applications such specific embodiments, without undueexperimentation, without departing from the general concept of thepresent invention. Therefore, such adaptations and modifications areintended to be within the meaning and range of equivalents of thedisclosed embodiments, based on the teaching and guidance presentedherein. It is to be understood that the phraseology or terminologyherein is for the purpose of description and not of limitation, suchthat the terminology or phraseology of the present specification is tobe interpreted by the skilled artisan in light of the teachings andguidance.

The breadth and scope of the present invention should not be limited byany of the above-described exemplary embodiments, but should be definedonly in accordance with the following claims and their equivalents.

1. A particle detector, comprising: (a) a first chamber wherein analyteparticles are subjected to a first particle detection mechanism; and (b)a second chamber, coupled to the first chamber, wherein the analyteparticles are subjected to a second particle detection mechanism, andwherein detection characteristics of the second particle detectionmechanism are orthogonal to detection characteristics of the firstparticle detection mechanism.
 2. The particle detector of claim 1,further comprising a control module coupled to the first chamber and thesecond chamber.
 3. The particle detector of claim 1, further comprisinga shutter between the first chamber and the second chamber, wherein theshutter is selectively opened, and wherein the analyte particles enterthe second chamber when the shutter is open and the analyte particles donot enter the second chamber when the shutter is closed.
 4. The particledetector of claim 3, wherein the shutter is selectively opened when apredetermined composition of analyte particles is detected in the firstchamber.
 5. The particle detector of claim 1, further comprising adisplay.
 6. The particle detector of claim 1, wherein the first particledetection mechanism is Ion Mobility Spectroscopy (IMS).
 7. The particledetector of claim 1, wherein the second particle detection mechanism isSurface Enhanced Raman Spectroscopy (SERS).
 8. The particle detector ofclaim 7, wherein the second chamber includes a ion beam focusing device.9. The particle detector of claim 7, wherein the second chamber includesa substrate refresher device.
 10. A particle detection method,comprising: (a) detecting presence of at least one predeterminedparticle type in an analyte particle sample using a first particledetection mechanism; and (b) confirming the presence of thepredetermined particle type in the analyte particle sample using asecond particle detection mechanism, wherein detection characteristicsof the second particle detection mechanism are orthogonal to detectioncharacteristics of the first detection mechanism.
 11. The particledetection method of claim 10, wherein the first particle detectionmechanism is IMS.
 12. The particle detection method of claim 10, whereinthe second particle detection mechanism is SERS.
 13. A computerimplemented method for analyzing particle data, comprising: (a)receiving first particle data, wherein the first particle data includesparticle data obtained by subjecting an analyte particle sample to afirst particle detection mechanism; (b) receiving second particle data,wherein the second particle data includes particle data obtained bysubjecting the analyte particle sample to a second particle detectionmechanism, wherein detection characteristics of the second particledetection mechanism are orthogonal to detection characteristics of thefirst particle detection mechanism; and (c) combining the first particledata and the second particle data to obtain combined particle data,wherein the combined particle data identifies particle types in theanalyte particle sample.
 14. The method of claim 13, further comprisingdisplaying, in a two-dimensional graph, composition of the analyteparticle sample determined by the first particle detection mechanism andthe second particle detection mechanism.
 15. A computer program productcomprising a computer usable medium having computer program logicrecorded thereon for enabling a processor to process particle data, saidcomputer program logic comprising: (a) first receiving means forenabling a processor to receive first particle data from a firstparticle detection device; (b) second receiving means for enabling aprocessor to receive second particle data from a second particledetection device, wherein the second particle detection mechanism isorthogonal with respect to detection characteristics to the firstparticle detection mechanism; and (c) means for enabling a processor tocombine the first particle data and the second particle data.
 16. Thecomputer program product of claim 15, wherein said computer programproduct further comprises means for enabling a processor to displayresults of combining first particle data and second particle data.